This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Current CPUs, information processors and other silicon and semiconductor based devices require thermal management for optimal performance. The reliability and performance of these CPUs decreases as temperature increases. Temperatures can be decreased by reducing clock rates, lowering device voltages, increasing airflow, or otherwise decreasing device temperature. Each of these solutions, however, is taxing on the efficiency of the given operating system or creates other negative effects. For example, a fan may cause unacceptable noise levels and its speed may need to be controlled to minimize noise level while maintaining an acceptable temperature. As another example, in semiconductor testing, the temperature of the device under test with widely varying power dissipation must be maintained within a prescribed range. Accurately measuring device temperatures ensures that temperature controlling solutions are implemented optimally. Therefore, an accurate, precise and fast acting temperature feedback scheme is essential to achieving maximum efficiency and performance levels while keeping electrical noise levels to a minimum.
In many instances, a device under test is an integrated circuit, which includes a die. The die comprises semiconducting material, which needs to be monitored for temperature. Temperature sensing of integrated circuit dice, for instance, can come in many forms. One such form of temperature sensor is a diode temperature sensor. Diode temperature sensors are provided within, on, or in proximity to the die or device under test being measured for temperature. Diodes are used as temperature sensors because the forward voltage across the diode is indicative of the temperature of the environment in proximity to the diode. If a diode is placed in, on, or near a die, the forward voltage across the diode is indicative of temperature of the die. When a fixed forcing current IF is applied through the diode junction, a simple equation relating forward voltage of the diode and temperature is given as:
                    T        =                                            C              1                        -                          V              F                                            C            2                                              (        1        )            
In Equation (1), T is the temperature in kelvin, VF is the forward voltage across a diode and C1 and C2 are constants that may be empirically defined. These constants C1 and C2, however, vary from device to device and require calibration to determine. Because calibration for specific devices is required, this method is highly impractical in a high-volume production process.
The forward voltage across a diode VF is expressed as:VF=(nkT/q)ln(IF/IS)  (2)where Is is the saturation current, q is the electron charge (1.6*10−19 Coulombs), k is Boltzmann's constant (1.38*10−23 J/° K), n is the ideality constant, and T is the temperature in kelvin. When a known forward current flows through the diode, one can measure the forward voltage VF. One can then calculate the diode temperature if the actual values for the saturation current Is are known. The saturation current Is, however, is very process dependent and also varies with temperature.
Another temperature measurement technique known in the art simplifies the calibration process by using two known current sources with a fixed ratio of N, allowing the effect of the saturation current Is to be eliminated. This is done by taking a forward voltage measurement when the forcing current IF passes through the diode, and taking a second voltage measurement when current N*IF passes through the diode. As shown by the following expression, the difference in forward voltage obtained by dividing one measurement by the other is a function of the temperature and does not depend on saturation current Is.(VF2−VF1)=(nkT/q)ln(N)  (3)
This method, however, has several disadvantages. First, for a temperature change in the order of 1 kelvin, the corresponding voltage difference change obtained using this measurement technique is three to four orders of magnitude smaller than the magnitude of the diode drop voltage. Further, the resistance of the conductor leads that provide the current to the diode and detect the voltage drop can induce significant error to the measurement. The effect of lead resistance can be removed by making yet a third measurement with a forcing current different than the first two, but the process grows more complex with the requirement of three very precise measurements. Second, the need to switch current level for each temperature measurement slows down the operation of the temperature management system by limiting the sampling speed due to the settling time and filtering requirement at each current level. Third, rapid switching of current in the diode can generate unacceptable electrical noise in the IC chip. Finally, in a situation where the temperature is changing significantly between measurements, the saturation current Is also changes significantly between measurements. Thus, the cancellation in the process is not valid and the measurements are erroneous.
Takashima et al., “Investigation on the Diode Temperature-Sensor with the Output Voltage Proportional to the Absolute Temperature,” IEEJ Trans. SM, Vol. 127, No. 6 (2007) discloses a technique intended to obtain an output voltage proportional to the absolute temperature using a diode sensor, wherein an ac voltage change in the diode due to temperature change is measured for a constant amplitude of an ac current superimposed on a forward dc current. Takashima principally discloses application of a square wave from which peak to peak measurements of the resulting output voltages can be determined. Such technique is substantially the same as the above-noted technique in which two forcing currents are applied to a diode sensor and is susceptible to the drawbacks previously described. Further, the technique disclosed by Takashima does not allow a rapid response to temperature changes in a device and fails to compensate for lead resistance associated with the diode sensor.
Accordingly, what is desired is a temperature sensing diode apparatus, method and system that can measure temperature in a faster and more efficient process, while keeping noise interference to a minimum. Further, it is desired to provide accurate dynamic temperature data in processes that require rapid, responsive temperature control.